The present invention relates to a carbon material and a method of preparing the same, and more particularly to a carbon material usable in the field of chemical and electronics in the next generation.
In the prior art, as carbon materials, there have been known carbon black, amorphous carbon, glass carbon, graphite, and diamond. Carbon black, amorphous carbon and glass carbon are carbon materials without a constant periodical structure.
By contrast, graphite comprises laminations of carbocyclic meshed two dimensional sheets, adjacent two of which are displaced by a half period from each other which provides two dimensional electrical conductivity. The bulk structure of graphite and properties thereof have been well known. Diamond has a three dimensional crystal structure so called as diamond structure which has a high strength widely useable.
Recently, however, as new carbon materials other than the conventional carbon materials, fullerenes such as C.sub.60 and carbon nanotubes have been on receipt of a great deal of attention. In Nature, vol. 318, pp. 162-163, 1985, it is disclosed that C.sub.60 comprises 60 carbon atoms in the form of football or soccerball. C.sub.60 has a high symmetry of electron structure which allows C.sub.60 to show various properties such as semiconductor properties, electrical conductance properties and super-conductance properties, for which reason C.sub.60 is attractive accordingly.
A carbon nanotube comprises a plurality of co-axial cylinders of graphite sheets. A carbon nanotube has a diameter in the order of a nanometer. Although carbon tubes of micrometer order in diameter have long been known, a carbon nanotube was first reported in Nature, vol. 354, pp. 56-58, 1985. Carbon nanotubes have received a great deal of attention as being applicable to one-dimensional conductive wire, catalyst, super-reinforced structure.
Particularly, electrical properties of each graphite sheet cylinder of the carbon nanotube depend upon the diameter and helical structure thereof. Those electrical properties are variable in the range from metal to semiconductors with various energy band gaps, for which reason the carbon nanotube is extremely attractive. Nature, vol. 382, pp. 54-56, 1996 reported that individual carbon nanotubes differing in structure show unexpectably various electrical properties. These facts were confirmed by measurement of electrical conductivity using four-probe circuits made by lithography. Recently, Nature, vol. 381, pp. 678-680, 1996 reported that a larger rigidity of carbon nanotube than diamond was theoretically expected and experimentally confirmed.
Following to the discovery of properties of fullerene and carbon nanotube, any new carbon material has been investigated. One of the new carbon materials is disclosed in Japanese laid-open patent publication No. 6-257019 which has a micro-geometric structure formed by cutting and folding a graphite sheet along a symmetrical axis thereof.
The above micro-structure of the graphite is considered as folding paper so call "Origami". The structure was experimentally explicated by atomic force microscopy and scanning tunneling microscopy. The above micro-structure of the graphite is disclosed in Nature, vol. 367, pp. 148-151, 1995 and Advanced Materials, vol. 76, pp. 582-586, 1995.
Recently, a graphite ribbon as a simplest model of the graphite folding papers "Graphite Origami" was theoretically calculated to find its specific and unique properties different from the conventional graphite. This is disclosed in Surface, Vol. 34(4), pp. 49-56, 1996.
The graphite ribbon is a graphite strip as one dimensional graphite with a finite size, whilst the normal graphite sheet is a two-dimensional sheet with infinite size.
The properties of the graphite ribbon largely depend upon its edge structure. The most typical edge structures are, as illustrated in FIG. 1, armchair edge and zigzag edge. The former edge is obtained when the graphite sheet is cut in a direction parallel to C--C bonding, whilst the later edge is obtained when the graphite sheet is cut in a direction vertical to C--C bonding.
In accordance with band calculation, when the width of the graphite ribbon having the armchair edge is widen, a metal appears every three and an insulator appears in other cases. When the insulator appears, as the width of the graphite ribbon is increased, the band gap is decreased so that the graphite ribbon might be regarded as a semiconductor. Such periodic properties are unique electron properties when conceiving the carbon nanotube.
On the other hand, the graphite ribbon with the zigzag edge shows a peak of density of state in the vicinity of the Fermi level which represents localization. Unstability on Fermi surface is caused, resulting in generation of finite magnetization. It is presumed that a local ferromagnetic order appears. Ferromagnetic property could never appear in the infinite two dimensional graphite sheet.
For the above reasons, expectations to the graphite ribbon and graphite folding paper "Graphite Origami" are possible.
However, the conventional carbon materials have some problems as described above. It is not easy to apply carbon black, amorphous carbon and glass carbon as well as graphite and diamond to the electronic devices. Carbon black, amorphous carbon and glass carbon area without periodic structure, for which reason there is variation in property over positions and it is difficult to obtain a constant and specific property. It has not been known to form a micro-structure of graphite and diamond.
The fullerene is required to be doped with n-type dopant such as alkali metals for application to superconductor and electrical conductor. The compound of fullerene is hard to be dealt with due to its unstability in the atmosphere. No certain and useful technical has been developed for perfect and stable crystal structure in desired area.
Carbon nanotube is applicable to quantum line due to its specific and unique properties and is the most expectable carbon material. Notwithstanding, the shape of the carbon nanotube is limited in shape to the cylinder. It is also difficult to form the carbon nanotube with desired size in the nanometer order.
On the other hand, graphite folding paper "Graphite Origami" has large freedoms in shape and size. Strip, right angle triangle, equilateral triangle, and combinations thereof, multiply folded one are, for example, available. Various size of the graphite folding paper may also be available. This means that the graphite folding paper "Graphite Origami" possess various new properties. Such structure may be formed by cutting and folding the graphite by atomic force microscopy and scanning tunneling microscopy. This is disclosed in Japanese laid-open patent publication No. 6-257019.
The manufacturing of graphite folding paper "Graphite Origami" using atomic force microscopy and scanning tunneling microscopy causes the problems with disturbance of edge in atomic level and the damaging or breaking the graphite.